Field of the Invention
Embodiments of the present application relates to the art of a control system for a drive unit that distributes output torque of a prime mover to a right and left wheels having a torque vectoring device for controlling a torque distribution ratio.
Discussion of the Related Art
U.S. Patent Publication No. 2014/162842 describes a torque vectoring device including a differential mechanism for distributing torque of a prime mover to right and left wheels, and a differential motor for applying torque to one of rotary elements of the differential mechanism to control distribution of the torque to the right and left wheels. PCT international publication WO 2015/008661 also describes a drive gear unit of this kind.
U.S. Patent Publication No. 2014/162842 further describes a control system configured to compute a required torque for the differential motor. According to the teachings of U.S. Patent Publication No. 2014/162842, the required torque for the differential motor is calculated based on programs of vehicle stability, traction performance, regeneration control, hybrid control, yaw damping etc., and variables representing the current vehicle state calculated based on detection signals from sensors. In the control system taught by U.S. Patent Publication No. 2014/162842, different programs are executed simultaneously and hence different required torques for the differential motor may be calculated by those programs. In this case, the arbitration functionality selects one of the required torques calculated by the different programs.
According to the teachings of U.S. Patent Publication No. 2014/162842, a motor having a generating function is used as the prime mover, and hence a braking force may be established by regenerating energy by the motor. In a vehicle using the torque vectoring device taught by U.S. Patent Publication No. 2014/162842, a distribution ratio of the braking force to the right and left wheels may be controlled by controlling the differential motor during regeneration of the motor.
In the conventional vehicles, a mechanical brake such as a friction brake is used to apply braking force to the wheels when stopping the vehicle. However, if such mechanical brake is arranged individually for each of the wheel, those brakes have to be controlled by a specific program. Especially, in a case of establishing a braking force by regenerating energy by the motor while establishing a braking force by the mechanical brakes in the vehicle having the torque vectoring device taught by the above-mentioned prior art documents, a complex control is required to control the torque vectoring device and the mechanical brakes cooperatively.